U.S. patent number 4,074,528 [Application Number 05/710,802] was granted by the patent office on 1978-02-21 for hydraulic control system with priority flow control.
This patent grant is currently assigned to J. I. Case Company. Invention is credited to Ramkishan Khatti, Patrick M. Lourigan.
United States Patent |
4,074,528 |
Lourigan , et al. |
February 21, 1978 |
Hydraulic control system with priority flow control
Abstract
A hydraulic control system for controlling the flow between a
reservoir, a pump having pressure flow compensating means
associated therewith and first and second flow control means for
controlling flow to first and second fluid operated devices is
disclosed herein. The hydraulic control system includes a priority
flow control valve which maintains a priority of flow from the pump
to the first flow control means based upon the amount of flow
required as well as the pressure requirements. The priority flow
control valve has a valve spool which is positioned as a function
of a biasing spring, as well as the pressure of the fluid from the
pump to the first flow control means and the pressure of the fluid
in the first fluid operated device. The system is particularly
adapted for functions requiring higher pressure than low stand-by
system pressure and where one of those functions require priority
over the other.
Inventors: |
Lourigan; Patrick M. (Kenosha,
WI), Khatti; Ramkishan (Racine, WI) |
Assignee: |
J. I. Case Company (Racine,
WI)
|
Family
ID: |
24855608 |
Appl.
No.: |
05/710,802 |
Filed: |
August 2, 1976 |
Current U.S.
Class: |
60/422;
60/445 |
Current CPC
Class: |
F15B
13/022 (20130101) |
Current International
Class: |
F15B
13/02 (20060101); F15B 13/00 (20060101); F15B
011/20 () |
Field of
Search: |
;60/422,445,448,452,484 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Geoghegan; Edgar W.
Attorney, Agent or Firm: Dressler, Goldsmith, Clement,
Gordon & Shore, Ltd.
Claims
What is claimed is:
1. A hydraulic control system including a reservoir, a pump having
pressure compensating means associated therewith, first and second
flow control means controlling flow to first and second fluid
operated devices and a priority flow control valve between said
flow control means and said pump, said priority flow control valve
including a housing having a valve bore therein with a valve spool
slidable in said valve bore and cooperating therewith to define
first and second chambers on opposite ends of said spool, biasing
means in said first chamber biasing said spool to a first position,
said housing having an inlet port connected to said pump and
communicating with said bore and first and second outlet ports
respectively connected to said first and second flow control means,
said first outlet port being in communication with said inlet port
when said valve spool is in said first position while said valve
spool blocks flow to said second outlet port, means connecting said
first outlet port to said second chamber, connection means between
said first fluid operated device and said pressure compensating
means providing pilot pressure flow from said first fluid operated
device to said pressure compensating means when said first control
means is in either actuated position to operate said pump as a
function of the pressure of fluid in said first fluid operated
device, said connection means being connected to said first chamber
so that said valve spool is moved as a function of the pump
pressure, the pilot pressure and the biasing means, unidirectional
valve means in said connection means preventing flow from said
pressure compensating means to said first chamber and said first
fluid operated device, said second fluid operated device including
first and second fluid operated brake actuating means with first
and second conduits connecting said first and second fluid operated
brake actuating means to said second flow control means, a branch
conduit between said first and second conduits having a pair of
opposed unidirectional valves therein preventing flow between said
first and second conduits and unidirectional valve means connected
to said branch conduit between said opposed unidirectional valves
and to said pressure compensating means for preventing flow from
said pressure compensating means to said first and second fluid
operated brake actuating means.
2. A hydraulic control system as defined in claim 1, in which said
second flow control means includes a brake valve having a housing
with a brake inlet, further including a housing attachment
connected to said brake valve and having a bore extending
therethrough and connected at one end with said second outlet port
and at the opposite end connected to said brake inlet, said bore
having a spring biased ball check valve therein preventing flow
from said brake actuating means to said pressure compensating
means, said housing attachment having passage means extending from
said bore and connected to said first and second fluid operated
brake actuating means and a ball freely movable in said passage
means and having first and second positions, said ball defining
said opposed unidirectional valves and said passage means defining
said branch conduit with said unidirectional valve means connected
to said passage means between said bore and said ball.
3. A hydraulic control system as defined in claim 2, further
including pressure responsive valve means in said passage means
between said unidirectional valve means and said ball, said
pressure responsive valve means being opened in response to
pressurized fluid in said bore, an additional conduit leading from
said passage means between said ball and said pressure responsive
means.
4. A hydraulic control system as defined in claim 1, in which said
second outlet port of said priority flow control valve is also
connected to an auxiliary valve for controlling flow to auxiliary
equipment.
5. A hydraulic control system as defined in claim 4, in which said
pump is connected to a hydraulically actuated transmission control
system for supplying fluid thereto.
Description
BACKGROUND OF THE INVENTION
The present invention relates generally to hydraulic control
systems that form part of a vehicle such as an agricultural
tractor. More particularly, the present invention relates to a
control system that incorporates a pressure-flow compensating pump
for delivering pressurized fluid to a plurality of fluid operated
devices with a priority flow control valve incorporated therein
that establishes priority of flow to a first fluid operated device
whenever the pressure or flow requirements for that device are
below a certain level.
Hydraulic control systems for controlling various functions that
form part of a vehicle such as a tractor have been in existence for
many years. Usually the hydraulic control system incorporates one
pump for supplying pressurized fluid to a plurality of devices.
Because of operational and safety reasons, it becomes necessary for
the control system to incorporate some type of priority flow
control to some of the devices. For example, in a tractor which
incorporates power steering and power brakes, it is essential that
at least one of these functions have priority for any flow that is
delivered from the pump so that the operator is at all times in
control of the vehicle.
In the past, the hydraulic control systems have normally been of
either the open-center system or the closed-center system. The
open-center system incorporates a fixed displacement pump that is
capable of delivering a maximum given flow required for the entire
system and a main control valve associated therewith connects the
pump directly to the reservoir when the valve is in the neutral
position. As expected in a system of this type, the pump is
constantly delivering full flow at low pressure when the control
valve is in a neutral position which results in considerable energy
loss.
Furthermore, in most hydraulic control systems of this type, the
system is designed to provide a maximum flow rate that is capable
of operating all of the fluid operated devices simultaneously. As
can be appreciated, the maximum flow rate for the pump is seldom
needed when operating a vehicle of the type under consideration.
Thus, in most instances, at least a portion of the power is wasted
since the system seldom demands the maximum flow of the pump and
the excess flow is bypassed through a pressure relief valve which
means that further energy is lost.
The closed-center system incorporates a variable displacement,
pressure compensated pump capable of a given maximum flow rate and
the system is always operated at a predetermined maximum pressure.
In this system, power is again wasted when less than the full
pressure is required for operating the devices to which pressurized
fluid is being supplied. In this system, the pump is constantly
operating at full pressure which may result in heating of the fluid
when the system is in a neutral position for extended periods of
time.
Quite recently a third type of system has been developed which may
be termed as a pressure-flow compensating or "load-sensing"
hydraulic system. This type of system is generally disclosed in
U.S. Pat. No. 3,486,334. The hydraulic circuit disclosed in this
patent consists of a variable displacement pump, the output of
which is controlled by a pressure compensating member that is
connected to the unit being controlled so that the pump produces
the required flow at the required pressure for delivery to the
controlled unit. This type of hydraulic circuit delivers low flow
at low pressure for minimum pump wear, flow losses and energy
losses when the main control valves associated therewith are in a
neutral position. The pressure-flow compensated hydraulic system
has the unique advantage of being capable of maintaining high
pressures without delivering a large volume of fluid and also
delivering large volumes of fluid at lower pressures as per
application needs. In other words, this system combines the
advantages of the open-center system and the constant-pressure
closed-center system while avoiding the major disadvantages.
While the pressure-flow compensating hydraulic system has numerous
advantages over the other systems described above, to date such
system has not found any widespread acceptance. At least one of the
reasons for the non-acceptance of such a system is the fact that in
the past, more expensive control valves and directional valves were
required in the hydraulic circuit utilizing the pressure-flow
compensating pump.
SUMMARY OF THE INVENTION
According to the present invention, there is provided a hydraulic
control system that includes a reservoir, a pump having pressure
compensating means associated therewith and first and second flow
control means controlling flow to first and second fluid operated
devices with a priority flow control valve in the system. The
priority flow control valve is designed to deliver all of the fluid
from the pump to the first fluid operated device whenever the
pressure or the flow requirements to that device are below a given
level.
The priority flow control valve includes a housing having a valve
bore with a valve spool slidable therein and cooperating therewith
to define first and second chambers on the opposite ends of the
spool. The priority flow control valve has an inlet port connected
to the pump and a first outlet port connected to a first flow
control means that controls the flow to a first fluid operated
device. A second outlet port on the priority control valve is
connected to a second flow control means which controls the flow of
fluid to a second fluid operated device.
The valve spool of the priority flow control valve is normally
biased to a first position by a spring in the first chamber and all
of the pressurized fluid from the pump is delivered to the first
outlet port when the valve spool is in the first position. The
pressurized fluid received in the first outlet port is delivered to
the second chamber on the opposite end of the valve spool so that
the spool is moved as a function of the pressure in the first
outlet port. A connection is provided between the first fluid
operated device and the pressure compensating means so that the
pump is operated as a function of the pressure and flow
requirements demanded by the first fluid operated device. This
connection is also in communication with the first chamber of the
priority valve so that the pressure in the connection means or
pilot conduit also controls the position of the valve spool in the
valve bore.
In the specific embodiment illustrated, the first fluid operated
device is a steering cylinder that forms part of the power steering
system for the vehicle while the second fluid operated device
consists of the operating means for the brakes that are normally
associated with the left and right-hand rear wheels of the vehicle
so that flow priority is developed to the steering system for the
vehicle.
According to another aspect of the present invention, all of the
necessary check valves associated with the secondary or brake
circuit portion of the hydraulic control system are housed in a
single control housing that can readily be attached to the housing
of a commercially available brake control valve, which greatly
simplifies the construction and assembly of the overall control
system.
The hydraulic control system can also be designed to provide
priority control flow to other fluid operated devices, as will be
explained in more detail later.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
FIG. 1 schematically illustrates the hydraulic control system of
the present invention with the priority flow control valve being
shown in cross-section;
FIG. 2 is a cross-sectional view of a portion of the hydraulic
control system that is associated with a commercially available
brake valve;
FIG. 3 is a vertical sectional view as viewed along line 3--3 of
FIG. 2.
DETAILED DESCRIPTION
While this invention is susceptible of embodiment in many different
forms, there is shown in the drawings and will herein be described
in detail a preferred embodiment of the invention with the
understanding that the present disclosure is to be considered as an
exemplification of the principles of the invention and is not
intended to limit the invention to the embodiment illustrated.
FIG. 1 of the drawings discloses a hydraulic control system,
generally designated by the reference numeral 10, having the
various features of the present invention incorporated therein.
Hydraulic control system 10 includes a reservoir 12 and a pump 14
having a pressure and flow compensating means 15 associated
therewith. Pump 14 is connected to reservoir 12 through a conduit
16 with the output of pump 14 delivered through conduit 18 to an
inlet port 20 of a priority flow control valve 22. Priority flow
control valve 22 includes a valve bore 24 extending through housing
26 with opposite ends of the valve bore closed by plug 28 and plate
or plug means 30. A valve spool 32 is slidably supported in valve
bore 24 and cooperates with housing 26 to define a first chamber 34
at one end of spool 32 and a second chamber 36 at the opposite end
of spool 34. Biasing means or spring 40 is located in chamber 34
and normally biases valve spool 32 to a first position, as will be
described in more detail later.
Valve housing 26 has a first outlet port 42 connected by conduit 44
to an inlet port 46 in a control valve means 48 that controls flow
of hydraulic fluid to and from a fluid operated device, such as a
fluid ram 50. Control valve means 48 is illustrated as being a
steering valve which controls the flow of fluid to opposite ends of
a steering cylinder and piston rod assembly that defines first
fluid operated device 50. Steering valve 48 is connected by a
return conduit 52 to reservoir 12 and also has first and second
outlet ports 54 and 56 respectively connected by conduits 58 and 60
to opposite ends of the cylinder that forms part of fluid ram 50.
Thus, actuation of the control valve in either direction from the
neutral position will pressurize one of the conduits 58 or 60 while
the second conduit will be connected to reservoir 12 through
conduit 52.
Fluid ram 50 is also connected to a pressure compensating means 15
associated with pump 14 through connection means which in the
illustrated embodiment consists of a conduit 64 connected to a
pilot port 66 in steering valve 48 with a unidirectional or ball
check valve 70 located in conduit 64 to prevent flow from pressure
compensating means 15 to fluid ram 50. Conduit 64 is also connected
by branch conduit 72 to the first chamber 34 having spring 40
therein while outlet port 42 of priority flow control valve 22 is
connected to second chamber 36 through an opening 74 in valve
housing 26.
Steering valve 48 may be a commercially available valve sold by
Ross Engineering under part No. HGA12006 with minor modifications
of such valve to provide a pilot port which is connected to either
end of the cylinder of the fluid ram 50 when the valve is actuated
in either direction from the neutral position. Alternatively,
steering valve 48 may be the above commercial valve without
modifications in which case conduits 58 and 60 would be connected
directly to conduit 64 with suitable check valve means associated
therewith such as check valves 94, 96 to be described later to
prevent flow between the two conduits 58 and 60 with a connection
to check valve 70 between the two valves to prevent flow from
conduit 64 to either conduit 58 or 60.
Control valve housing 26 has a second outlet port 76 connected by
conduit 78 to an inlet of second flow control means or brake valve
80. Brake valve 80 is a commercially available valve sold as part
No. 39300-AD by Cessna Corporation. Brake valve 80 has first and
second manually actuated valve spools 82 and 84 which, when
actuated, respectively supply pressurized fluid through conduits 86
and 88 to the left and right-hand brakes (not shown). In the
neutral position for the respective valve spools 82 and 84,
conduits 86 and 88 are connected to reservoir 12 through a return
conduit 90.
The brake circuit of the hydraulic control system also includes a
hydraulically actuated differential lock of the commercially known
type which is capable of interlocking the two wheels. This
differential lock is hydraulically actuated by supplying
pressurized fluid from a separate source to a control valve (not
shown). The differential lock is also interconnected with the
hydraulic circuit for the left and right-hand brakes so that the
differential lock is automatically released when either of the
brakes is actuated and both brake conduits are connected to
pressure compensating means 15 so that pump 14 may be operated as a
function of the pressure and flow requirements in either the left
or right-hand brake.
According to one aspect of the present invention, the
interconnection means between the brakes and the differential lock
as well as the pressure compensating means 15 are interrelated to
substantially simplify the number of parts and construction thereof
required for providing such interconnection.
As illustrated in FIG. 1, conduits 86 and 88 are interconnected by
a conduit 92 that has two oppositely directed unidirectional valves
94 and 96 located therein. These valves prevent flow between left
and right-hand conduits 86 and 88 but will accommodate flow from
either conduit to a differential lock conduit 98 connected to
conduit 92 between the two unidirectional check valves 94 and 96. A
further branch conduit 100 leads from between the two check valves
94 and 96 to pressure compensating means 15. Conduit 100 has a
unidirectional valve 102 therein which blocks flow from
compensating means 15 when the brake or secondary circuit is in a
neutral condition. Also, conduit 100 has a pressure responsive
check valve 104 located therein and this pressure responsive check
valve is opened in response to pressurization of the fluid is
conduit 78 leading from priority valve 22 to brake valve 80.
Whenever conduit 78 is pressurized, check valve 104 is held in an
open position to provide a direct connection from conduit 92 to
pressure compensating means 15 through unidirectional valve 102.
However, if the fluid is conduit 78 is not pressurized, check valve
104 will be closed and will prevent flow through conduit 100. This
allows the operator to provide manual braking power by manual
pressurization of the fluid in either conduits 86 or 88 to the
respective brakes should hydraulic power be lost.
According to one aspect of the invention, check valves 79, 94, 96,
102 and 104 are all incorporated into a single housing that can
readily be attached to the commercially available brake valve 80 to
convert the brake valve to a control valve means that can be
utilized with a pressure compensating pump. This arrangement
simplifies the construction of the system and reduces the overall
cost of the system.
The details of the valve attachment are illustrated in FIGS. 2 and
3. The valve attachment consists of a valve housing 120 that may be
connected directly to the housing of brake valve 80 by bolts 121
and housing 120 has an inlet bore 122 extending therethrough with
an enlarged portion 124 at one end thereof. The enlarged portion
124 supports a ball check valve 126 that is biased to a closed
position by a spring 128 and defines unidirectional valve means 79,
illustrated in FIG. 1. A suitable fitting 129 is threaded into the
opposite end of bore 122 for providing a connection to conduit 78
leading to housing 120. Inlet bore or port 122 has a transverse
passage 130 extending therefrom with a rod 132 slidably supported
in passage 130. The opposite end of passage 130 has an enlarged
portion 130a which receives a threaded fitting 134 therein that is
capable of having conduit 98 connected thereto for connection to
the circuit for the differential lock (not shown). A spring biased
spool 136 is biased by a spring 138 into engagement with a value
seat defined at the end of an enlarged portion 130a of passage 130.
Rod 132 and valve element 136 define pressure responsive valve
means 104 illustrated in FIG. 1.
Valve passage 130 has a further intermediate sized portion 142 that
is in communication with a further bore 144 having a threaded
fitting 146 at the outer end thereof for connection of conduit 100
thereto. A further spring biased valve element 148 is biased into
engagement with a valve seat by a spring 149. Vavle element 148 and
spring 149 define pilot check valve 102 illustrated in FIG. 1.
The enlarged portion 130a of passage 130 is also connected by
passage means 150 to a further passage 152 that extends from one
end of housing 120 to the opposite end. Passage 152 is closed at
both ends by respective plug members 154 and 156 and has a freely
movable ball 158 located between the inner ends of the respective
plugs. Each plug has an axial opening 160 and a transverse opening
162 with the transverse openings being in communication with
perpendicular bores 164 and 166. Bores 164 and 166 extend to the
surface of valve housing 120 and have fittings 168 threadedly
received therein (only one being shown in FIG. 3). These fittings
168 respectively have conduits 86 and 88 connected thereto. Ball
158 and associated passages 150, 152 define both unidirectional
valve means 94 and 96 and conduit 92, illustrated in FIG. 1.
The operation of the circuit so far described will now be
summarized. Assuming that steering valve 48 and valve spools 82 and
84 of brake valve 80 are all in the neutral position, there will be
no demand for pressurized fluid from pump 14. The pump 14 will then
have a minimum flow output at a very low pressure, such as 200
p.s.i. to replenish any fluid leakage within the control system. In
this condition, spring 40 will bias valve spool 32 to the first
position wherein the flow of fluid from inlet port 20 to second
outlet port 76 is blocked. It should be noted that the spring force
for spring 40 is such that it is approximately equal to the fluid
force on valve spool 32 at the minimum level of 200 p.s.i. Also any
flow from first outlet port 42 is blocked by control valve 48.
If a steering function is to be performed, steering valve 48 will
be actuated so that pressurized fluid is being demanded either in
conduit 58 or conduit 60 while the other conduit will be connected
to reservoir 12 through conduit 52. When this condition occurs, the
conduit to be pressurized will be connected internally of valve 48
to pilot port 66 and the pressure of the fluid in such conduit will
be sensed by pressure compensating means 15. The pressure
compensating means 15 will actuate pump 14 to provide the necessary
flow of fluid at the required pressure through inlet port 20, valve
bore 24, outlet port 42 through valve 48 to the appropriate end of
the cylinder that forms part of fluid ram 50. At the same time, the
pressure of the fluid in port 42 is delivered through opening 74 to
the second chamber 36 to oppose spring force 40 while the pressure
of the fluid in conduit 64 is delivered to first chamber 34 to
assist spring 40 in maintaining the valve spool in the first
position. Thus, the pressure of the fluid in outlet port 42 must
reach a certain level before the valve spool can be moved from the
first position, to the right as viewed in FIG. 1, to allow fluid
under pressure to be delivered to the secondary port 76. Stated
another way, valve spool 32 is normally held in a first position,
when hydraulic fluid is demanded by steering valve 48 to block flow
to the secondary circuit consisting of brake valve 80 and the
movement of the valve spool from the first position is controlled
by the pressure of fluid in outlet port 42, the pressure of fluid
in the pilot conduit 64 as well as the spring force 40.
Assuming now that all of the pressure and flow requirements for
producing the desired steering functions are met, the pressure of
the fluid in outlet port 42 and opening 74 as well as chamber 36
will increase sufficiently to move the valve spool 32 to the right
as viewed in FIG. 1 and, therefore, connect inlet port 20 to second
outlet port 76 so that pressurized fluid from pump 14 is available
for actuating either the left or right-hand brake. Assuming now
that one of the brake spools 82 or 84, such as brake spool 82, is
actuated, such actuation will produce a demand for pressurized
fluid in conduit 86. This demand for pressurized fluid will be
sensed by pressure compensating means 15 through check valve 94,
pressure responsive valve 104 (which is now held open by the
pressure of fluid in conduit 78), check valve 102 and conduit 100.
The drop in pressure within conduit 86 will produce a demand for
increased pump output from pump 14 so that pump 14 will produce the
desired amount of fluid at the required pressure for actuating the
brake.
If there is no demand for pressurized fluid to steering valve 48,
any pressure demands for fluid to conduit 78 will also be delivered
through opening 74 to chamber 36 to cause valve spool 32 to move to
the right, as viewed in FIG. 1, to a position where ultimately
first outlet port 42 will be blocked by valve spool 32 and all of
the fluid from pump 14 will be delivered to second outlet port 76
and ultimately to brake valve 80.
Thus, it will be appreciated from the above description that the
present hydraulic control system provides a very simple arrangement
for providing priority flow to one of two fluid operated
components. If desired, this same system can also be utilized to
provide pressurized fluid for various other functions. For example,
as illustrated in FIG. 1, conduit 78 could be connected to a
further auxiliary control valve 200 which could be connected to
reservoir 12 by a conduit 202 and to pressure compensating means 15
through a conduit 204 having a unidirectional valve 206 therein.
The auxiliary valve could be part of the circuit that provides
pressurized fluid to hydraulic components, such as the draft
control system for the vehicle or pressurized fluid to trailing
implements, such as tilling devices which are hydraulically
actuated. If desired, a pressure regulating valve could be located
between conduit 78 and control valve 200 to prevent flow to control
valve 200 when the pressure of the fluid in conduit 78 is below a
certain level required for actuation of the brakes. This would
insure priority of flow to the secondary circuit consisting of
brake valve 80 before fluid is available for operating the
auxiliary circuit.
It is also contemplated within the spirit of this invention that a
further control valve 200 could be replaced with a further priority
control valve 22 and, therefore, two additional hydraulic circuits
could be controlled with a single pump. Again, priority of flow
could be established for one of the two circuits as explained with
respect to the basic hydraulic control circuit disclosed
herein.
The same hydraulic control system can also be utilized for
supplying pressurized fluid to other fluid operated circuits which
require very low pressure. For example, hydraulically actuated
transmissions of the type incorporated into many agricultural
tractors of the type under consideration can be actuated by fluid
pressure that is pressurized to less than 200 p.s.i. Thus, in the
control system illustrated and described above, the conduit 18
could be connected directly to a transmission circuit 210 and
provide the necessary pressurized fluid for actuating the various
hydraulic components in the transmission. This arrangement would
not in any way deter from the priority of flow to the steering
valve 48 since any demand for fluid to the steering valve would
automatically increase the pressure in conduit 18.
It should also be realized that while the two fluid operated
devices have respectively been illustrated as a steering ram 50 and
left and right-hand brakes, the system could readily be designed
for providing priority flow to any particular function, such as a
brake circuit with other functions, or a steering system with other
functions such as a remote hydraulic system associated with an
implement and a draft control circuit that controls the movement of
a hitch on the tractor.
* * * * *